tire/wheel sizing ques. for V8 vs. 5kcs + FUN MATH!

[Bryan Kamerer <kamerer@madriver.com>]

	I have received much help from the list regarding getting a 5kcsq or tq
for (harsh) winter duty in place of the V8.  Have likely narrowed it down
to two candidates and now I need some tire advice:

1) I have factory BBS 15x7.5 V8/200tq wheels mounted with yoko snows.  Will
they work on a 5kcstq?  Bolts are same (5 x 112mm), 

a) is offset compatible with fenders and 215/60-15 tires when mounted up to
5kcstq?  
b) offset is 36mm, I believe, on V8/200tq wheels.

2) How much speedo error induced by size assuming the tires fit?

is it (using 25.4mm/inch where conversion necessary, right?):

total oversize tire diameter - oem tire diameter / oem tire diameter x 100 ?

thus 25.15" (15" + 215mm x 0.60 x2) - 24.68" (15" - 205mm x 0.60 x 2) /
24.68 ?

so that would be only a 1% error (to the underside (pessimistic) since the
tire is larger, thus the speedo not turning over as often as the tire is
now covering it really is moving?).  tire is now 79.01" in circumference
(each revolution) vs. 77.53" for the 205/60-15.  Actually, it seems if you
look at it on a circumference basis, then the error is more like 2% since
the diff is 2% on the cicumferenec measurements (which I guess is what
really counts, 79.01" vs. 77.53")  Ok, I think I answered my own question
and realized I am slightly mistaken above, but the answer is n more than
2%, right?

This isn't as sexy as those air flow/mm HG/etc. turbo math thingy's we see
the real rocket scientists on the list do, but hey, this is as fancy as it
gets for this liberal arts major.

I read about this once long ago but am just working through it by logic now
and  would appreciate someone more thorough double checking me.

Thanks alot!

Bryan Kamerer
V8/5spd.
5kcstq (real soon, I hope)